1. Field of the Invention
The present invention relates to a reciprocating compressor, and more particularly, to a piston displacement device for a reciprocating compressor capable of minimizing a dead volume by moving a piston according to a capacitance variation of a compressor and thereby increasing an efficiency of the compressor.
2. Description of the Conventional Art
Generally, a reciprocating compressor is a device for sucking gas, compressing, and discharging the gas as a piston is linearly reciprocated in a cylinder. FIG. 1 is a sectional view showing an example of a reciprocating compressor in accordance with the conventional art.
As shown, the conventional reciprocating compressor comprises a casing 10 having a gas suction pipe SP and a gas discharge pipe DP, a frame unit 20 elastically supported in the casing 10, a reciprocating motor 30 supported by the frame unit 20 and fixed in the casing 10, a compression unit 40 for sucking and compressing refrigerant gas while a piston 42 is linearly reciprocated with a mover 33 of the reciprocating motor 30, and a resonance spring unit 50 for inducing a resonance by elastically supporting the reciprocating motor 30.
The frame unit 20 includes a front frame 21 for supporting each one side of an outer stator 31 and an inner stator 32 of the reciprocating motor 30 and for supporting a cylinder 41 and the piston 42 of the compression unit 40, a middle frame 22 coupled to the front frame 21 under a state that the reciprocating motor 30 is interposed therebetween for supporting the outer stator 31 of the reciprocating motor 30, and a rear frame 23 coupled to the middle frame 22 for supporting the resonance spring unit 50.
The reciprocating motor 30 includes the outer stator 31 having a winding coil C and fixed between the front frame 21 and the middle frame 22, the inner stator 32 positioned at an inner side of the outer stator 31 and fixed to the cylinder 41 of the compression unit 40, and the mover 33 having a magnet M and linearly reciprocated between the outer stator 31 and the inner stator 32 along a flux direction.
The compression unit 40 includes the cylinder 41 insertion-coupled to the front frame 21, the piston 42 coupled to the mover 33 of the reciprocating motor 30 and reciprocated in the cylinder 41 for sucking and compressing refrigerant gas through a gas channel F, a suction valve 43 mounted at an end of the cylinder 41 for opening and closing the gas channel F, a discharge valve 44 detachably installed at an end of the cylinder 41 for limiting the discharge of compression gas, a valve spring 45 for elastically supporting the discharge valve 44, and a discharge cover 46 having the discharge valve 44 and the valve spring 45 therein and fixed to the front frame 21 with the cylinder 41.
The resonance spring unit 50 includes a spring supporting unit 51 coupled to a connection part between the mover 33 and the piston 42, a plurality of front resonance springs 52 for supporting the front side of the spring supporting unit 51, and a plurality of rear resonance springs 53 for supporting the rear side of the spring supporting unit 51.
An unexplained reference numeral P denotes a compression chamber.
An operation of the conventional reciprocating compressor will be explained as follows.
When power is applied to the outer stator 31 of the reciprocating motor 30, a flux is generated between the outer stator 31 and the inner stator 32 and thereby the mover 33 and the piston 42 move in the flux direction. Accordingly, the piston 42 is linearly reciprocated in the cylinder 41 by the spring unit 50 and generates a pressure difference in the compression chamber P of the cylinder 41, thereby sucking refrigerant gas into the compression chamber P, compressing the gas into a certain pressure, and discharging the gas. The processes for sucking, compressing, and discharging the gas are repeated.
In order to control a cooling capacity of the compressor according to a load condition of a refrigerating cycle, an amount of current supplied to the winding coil C is controlled so as to control a stroke length of the piston 42. Accordingly, a suction amount of refrigerant gas is increase or decreased so as to control the cooling capacity according to the load.
However, in the conventional reciprocating compressor, as shown in FIGS. 2 and 3, as the stroke length of the piston 42 is varied, a top dead center (TDC) is spaced from the discharge valve 44 thereby to increase a dead volume. Especially, in case of shortening the stroke length by reducing the amount of current supplied to the winding coil C in order to decrease the cooling capacity of the compressor, the top dead center of the piston 42 is more spaced from the discharge valve 44 thereby to lower the efficiency of the compressor.